1. Field of the Invention
This invention relates to a liquid sealing and vibration isolating apparatus such as a suspension mounting rubber and an engine mounting rubber of a vehicle and, more particularly, to a liquid sealing and vibration isolating apparatus which can display the non-linear characteristics.
2. Description of the Prior Art
As one example of such a liquid sealing and vibration isolating apparatus, Japanese Patent Unexamined Publication No. 64-1566 discloses a first bracket attached to a body side, a second bracket attached to a side of a vibrating member, a rubber portion provided between the two brackets, a liquid chamber provided in the rubber portion, and a rubber partition wall dividing the liquid chamber into two chambers, wherein the rubber partition wall is integrally formed with an orifice portion communicating with the two liquid chambers and a membrane portion with a thin center portion.
In such a liquid sealing and vibration isolating apparatus, it is desirable to display both low dynamic spring characteristic and high vibration damping characteristic wherein the low dynamic spring characteristic is for effectively absorbing the vibration input of higher frequency with smaller amplitude (hereinafter referred to as small vibration) such as an engine vibration, while the high vibration damping characteristic is for obtaining sufficient damping when the vibration of lower frequency with smaller amplitude such as shake vibration resulting from tire unbalance and the vibration of lower frequency with larger amplitude (hereinafter referred to as large vibration) such as a vibration input from a suspension side in response to the input of irregularities in a road surface.
By the way, it is possible to make the conventional liquid sealing and vibration damping apparatus described above in low dynamic spring condition by decreasing spring constant of the membrane portion, but if the deformation of the membrane portion remains unchanged, it becomes not possible to obtain sufficient high vibration damping since the elastic deformation of the membrane portion also becomes larger accordingly when the large vibration is input. Accordingly, it becomes practically necessary to provide the membrane portion with a deformation control portion for controlling the deformation more than a predetermined stroke.
However, when the membrane portion is provided with such a deformation control portion, it is not only controlled from deforming, but also there is suddenly caused a damping force, thereby making a passenger feel a shock and a vehicle is sometimes uncomfortable to ride in. Also, since there is caused a striking sound whenever the membrane portion contacts with the deformation control portion, it may become a noise source.
Further, a stair-like change of the spring constant in such membrane portion means that the resonance frequency in the orifice portion also changes in such a stair-like manner and as a result, it becomes difficult to maintain the optimum resonance frequency in all area where the damping is needed. Still further, it is necessary in structure to increase the number of parts because of the provision of the deformation control portion.